Attempts by chemical means to deplete brain serotonin levels in experimental animals have utilized, for the most part, para-chlorophenylalanine (pCl-Phe), a potent and relatively specific inhibitor of tryptophan-5-hydroxylase. Furthermore, pCl-Phe treated maternal rats are known to almost invariably kill their pups. In an attempt to more directly link brain serotonin depletion and filicidal behavior, several different methods of lowering brain serotonin concentrations will be comparatively evaluated regarding their efficacies in decreasing brain serotonin and their capacities to induce filicide in lactating rats. The serotonin-depleting techniques to be investigated include: 1) blockage of the uptake of tryptophan into neuronal cells from the circulation, 2) inhibition of the availability of tryptophan to the serotonin biosynthetic system, 3) blockage of serotonin receptors with lysergic acid diethylamide, 4) blockage of serotonin receptors in the CNS with chemically different compounds, methysergide and Cinanserin, and 5) destruction of serotonergic neurons in the CNS by 5,6-dihydroxytryptamine.